1. Field of the Invention
The present invention relates to an improvement of cutting tool such as end mill and reamer having a twisted edge in the blade part, and more particularly to a cutting tool comprising a sintered compact of high hardness and high wear resistance buried and affixed in the blade part along the twisted edge, the sintered compact, such as polycrystalline diamond sinter and cubic boron nitride sinter, being higher in hardness and wear-resistance than its base material, and the manufacturing method of the cutting tool.
2. Description of the Prior Art
Hitherto, in order to meet the demands for enhancing cutting efficiency and prolonging tool life, cutting tools such as end mill and reamer having a sintered compact of diamond or cubic boron nitride in the blade part, the sintered compact being very high in hardness and excellent in wear resistance, have been developed and employed.
The sintered compact of high hardness and high wear resistance used in such conventional cutting tools is in a chip form shaped by sintering fine powder of diamond or cubic boron nitride at high temperature and high pressure. Besides, to facilitate bonding to the base material of the blade part such as cemented carbide and steel, the material powder of diamond or cubic boron nitride is not sintered alone, but it is sintered and formed on a substrate made of cemented carbide or the like. Thus formed sintered chip is about 0.5 mm in thickness, and is shaped in circular, semicircular, sector, triangular, rectangular or other thin plate form, and this sintered chip is soldered to the buried and affixed in part of the base material of the blade part.
Examples of such conventional cutting tools are shown in FIG. 6 and FIG. 7.
A straight edge end mill 1 in FIG. 6 comprises a blade 2 and a shank 3, and the blade 2 made of cemented carbide, steel or the like is provided with a front edge 4a and a side straight edge 4b. In the blade 2, moreover, two sintered chips 5 of high hardness and high wear resistance in semicircular plate form are buried and affixed by soldering so as to form part of the edges 4a, 4b at positions where much load is applied while machining, in particular.
A straight edge end mill 1a shown in FIG. 7 is formed exactly the same, in which two bar-shaped sintered chips 5 of high hardness and high wear resistance are buried and affixed so as to form part of the front edge 4a and the side straight edge 4b.
Such structure is quite the same in other cutting tools.
Thus, in all conventional cutting tools, a high hardness sintered chip such as diamond sinter and cubic boron nitride sinter is buried and affixed so as to form part of the straight edge, and the other part of this straight edge is made of its base material itself.
Besides, such cutting tools composed of the sintered chips of high hardness and high were resistance buried therein are almost limited to straight edge type, and can not have twisted edge such as end mill and reamer. This is because such a sintered chip is formed by sintering material particles at high temperature and superhigh pressure, and as a matter of course thus formed sintered chip is limited in its shape and size, and can not be in a twisted shape or be buried to form part of the twisted edge.
Moreover, when burying and affixing the sintered chip of diamond or cubic boron nitride to the base material of the blade by soldering, the chip is heated to a considerably high temperature, and the adverse effect by the heat cannot be ignored. In particular, in the case of a diamond sintered chip, heating may cause to form a graphite layer on the sintered chip surface and to burn the chip, so a sufficient caution is needed during work.
Yet, whether in diamond or in cubic boron nitride, soldering of the sintered chip and the base material may be peeled off by the heat during the process of machining.
On the other hand, cutting tools having a twisted edge on the flank of the blade part, for example, spiral end mills, are known to be more excellent in the cutting performance and the dimensional precision after cutting than the straight edge end mills.